That does look very stunning, I see what you mean by the holding drop, but I think B&M have probably thought out a system for how it would work otherwise wouldn't they be taking a bit of a risk with just the one chain? - The alternative aspect is might it not have the holding drop and just stop horizontally at the top of the lift, this I doubt but it's just an alternative thought though.

That looks absolutely stunning! Flows so well and in a way has a very similar start to Swarm with the Dive loop/Immelman going straight into the zero-g!

To answer the question about the holding break, it is most likely that the chain takes the cart to the holding brake where the car would swap onto a separate chain which will then hold the car in place. This would be done in a similar way to when there has to be 2 separate chains on a lift-hill where the car swaps chains almost immediately. There could also be a short crossover period with the car on both chains.